It's not fiction, it's real. Hackers came out way after people had already been doing this. Let me give you a few examples:
1) hacked credit bureau merchant accounts (dialup, + passwords) were routinely traded on hacker BBSes and voicemail boxes in the 80s. Using this, you could lookup someone via telephone number, name, or SSN and get their entire credit history, and from there, lookup their family's credit history, including all of their revolving accounts.
2) Using credit card information, you could either phone in orders to drop points and have some teenager pick up the stash, or, you could create a new credit card. A friend of mind who was an electrical engineer created a machine used to write new credit card magnetic strips on the back of any card. Another guy used a stolen ZOM machine (merchant machine to verify cards before Verifone came out) which performed a simple read and integrity check on the card. This integrity check is the well known "double mod 10" check-digit routine. The Z80 assembly code in the ZOM machine was disassembled to find out the encoding mechanism on the magnetic strip which is a self-clocking bi-polar code.
3) With this equipment in hand, you can make *physical* credit cards with someone else's info.
4) Possessing all of someone's personal data, you can call up the utility companies and deactive or activate services, since they would just query you about your address, phone, mother's maiden name, etc
5) In the days of blueboxes/purple boxes/rainbox boxes it was possible to get operator privileges, listen in on phone calls, shutdown active phone calls, (e.g. before call waiting, the "operator interruption" request)
6) Social engineering was quite easy in the days before the 90s internet. Few people were aware of hacking. All it took was a little knowledge of the target to breed familiarity, and an air of authority to get what you want.
Back in the 80s, Americans used to scam AT&T calling cards off people by the thousands. I knew a teenage guy whose voice hadn't changed and he sounded like a female operator on the phone. He would call up people, tell them there was something wrong with their bill and ask them for the last 4 digits of their calling card for verification (the first 10 are the phone number itself). These were then promptly traded to Europeans so they they could uploaded cracked 8-bit C64 warez to US bulletin boards in exchange. They would also use American calling cards to make free local calls within Europe.
Simply put: a twelve year old kid could *seriously fuck you up* in the 80s.